None of these Rosary memberships binds under the pain of sin. It is not even a venial sin to fail in this duty because such an undertaking is entirely voluntary and supererogatory. Needless to say, people should not join the Confraternity if they do not intend to fulfill their obligation by saying the Rosary as often as is required, without, however, neglecting the duties of their state in life…
And, my dear Catholic people, even if you fail to say your Rosary out of sheer carelessness or laziness, as long as you do not have any formal contempt for it, you do not sin, absolutely speaking…
–from The Secret of the Rosary by St. Louis De Montfort
Dear brothers, let us not fail to warn those in the Roman Catholic church to flee from it with its errors and heresies.